As if putting feathers on dinosaurs wasn't insult enough, a radical new theory from Paul Else of the University of Wollongong is proposing that dinosaurs produced a kind of milk for their offspring, that they essentially lactated — a physiological process that's associated almost exclusively with mammals. But as Else's new paper suggests, some modern birds feed their newly hatched young with secretions similar to the milk of mammals. So why not dinosaurs, too?

Indeed, pigeons, emperor penguins, and flamingos all produce a milk-like substance for their young. But rather than delivering food to their babies with breasts, these birds regurgitate the substance and transmit it mouth-to-mouth. Else hypothesizes that the dinosaurs did a similar thing.

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"Since birds and dinosaurs share much in common I proposed that some dinosaurs likely used this feeding strategy," he said in a statement.

It's important to note that this isn't just the regurgitation of previously consumed food (i.e. partially fermented plant matter). Some birds produce these secretions from various parts of their upper digestive tract, including the crop organ, esophageal lining, and proventriculus. The resulting "milk" is similar to what mammals produce; it contains similar levels of fat and protein, along with carotenoids, antibodies and, in the case of pigeons and doves, epidermal growth factor.

Else, a molecular biologist with an interest in membrane lipids, came up with the idea when considering how difficult it must have been for dinosaur parents weighing several tonnes to feed their relatively tiny offspring. Moreover, paleontologists know that dinosaur babies grew quickly, which, when considering Else's concern, presents a kind of conundrum. The only way it was possible, argues Else, was a form of lactation.

Else proposes that dinosaurs used secretory feeding to increase the rate of growth of their young (the "milk" may have contained growth hormone). And like mammalian breast milk, the secretions could have provided immune responses, among other benefits.

His new paper was just accepted for publication in The Journal of Experimental Biology. Moving forward, Else's hope is that a "real" dinosaur biologist will prove or disprove his theory — what could be easier said than done given the dearth of paleontological evidence in support of such an (apparent) wild claim.

But that said, he claims it might be possible to prove by studying dinosaurs like the herbivorous duck billed hadrosaur — dinosaurs that may have sustained their young — not with fermented plant matter — but with this specialized secretion.